1. Field of the Invention
The present invention relates to a helical antenna for use in mobile communications and local area networks (LAN).
2. Description of the Related Art
It is important for an antenna for use in mobile communications and local area networks to be small. As one type of antenna which satisfies such a demand, there is a normal-mode helical antenna. FIG. 6 shows the construction of the normal-mode helical antenna.
A normal-mode helical antenna 1 shown in FIG. 6 is formed in such a way that a linear conductor is wound so that a winding cross section 3 intersecting at right angles to a winding axis C is formed substantially in the shape of a circle, with a power feeding section 4 being provided on one end of the normal-mode helical antenna 1 and the other end being formed into a free end 5.
However, in the above-described conventional normal-mode helical antenna, since the relationship between the resonance frequency and the inductance components of a conductor has not been clarified, it is difficult to determine with ease the structural parameters of the conductor for obtaining a desired resonance frequency, for example, the winding cross section of the conductor, the number of windings of the conductor, or the coil length of the conductor, at the design stage.